The present invention relates to a method and apparatus for producing an ordered array of nanoparticles on a substrate surface and to a nanomaterial having such an ordered array of nanoparticles. Particularly, but not exclusively, the invention relates to the provision of an ordered array of magnetic nanocrystals on a substrate surface.
Although the present invention is not limited to the production of a magnetic array, one important object of the present invention is the production of a material suitable for use as an ultra high density magnetic data storage medium.
According to the present invention there is provided a method of producing a structure comprising a plurality of nanoparticles distributed across a surface of a substrate in a predetermined array, the method comprising the steps of:
i) providing a substrate which has a passivated surface;
ii) depositing nanoparticles on to said surface; and
iii) displacing said particles over said surface to configure them in said predetermined array.
The concept of a passivated surface is well known to those in the art. Essentially a passivated surface is one which has substantially no dangling bonds and thus will not form a bond with the nanoparticles deposited on the surface. Although there may still be van dea waal forces between the particles and the surface these will be insignificantly weak.
The substrate may be a passive material or may be a non-passive material in which case step (i) includes a preliminary step of passivating said surface.
Passivating surfaces is a well known procedure. Essentially, it comprises coating the surface with atoms which take up the available dangling bonds.
Said passivating step may comprise covering said surface with atoms of an element such as hydrogen, fluorine, chlorine or oxygen. Monovalent elements are preferred.
Preferably said nanoparticles are passivated. This prevents nanoparticles bonding to one another on the surface.
Preferably said nanoparticles are passivated by passing them through a chamber containing gaseous atoms of a suitable passivating element such that said nanoparticles are coated with said passivating atoms prior to being deposited on said surface. Gases of monovalent atoms are preferred, particularly hydrogen although other atoms, such as oxygen, may be used.
Alternatively the nanoparticles may be passivated by covering them with a passivating element after they are deposited on said surface prior to, or during, the displacing step (iii).
Preferably said substrate surface is provided with an array of predefined regions corresponding to said predetermined array and said step (iii) comprises displacing the nanoparticles so that they move into and are retained within said regions.
For instance the regions may be physical features such as pits or holes sized to receive and retain said nanoparticles. Alternatively the regions may be non-passivated regions which chemically bond to said nanoparticles.
Various methods suitable for displacing the nanoparticles into said regions are described further below.
Alternatively said displacing step (iii) comprises establishing a standing laser wave, or an array of standing waves, using a laser so as to produce low energy nodes at locations corresponding to said predetermined array, whereby said nanoparticles are displaced into regions of said surface coincident with said low energy nodes thereby adopting a configuration corresponding to said predetermined array.
Methods according to the present invention are particularly suited to the production of a structure comprising an array magnetic nanoparticles, such as clusters of ferromagnetic atoms (for example cobalt atoms), in a non-magnetic matrix. Such materials can be used as the basis of a ultra high density storage media.